Very generally speaking, the invention concerns the field of watch bracelets made of a hard material such as ceramic material and intended to be assembled to watches whose case includes an exterior made of hard material.
These structures have certain limits as to their application precisely because of the techniques used to manufacture them. Indeed, exterior parts made of hard materials, for example of ceramic material, are obtained by methods comprising a moulding step followed by a sintering step. During the sintering operation, these parts are subject to shrinkage, i.e. they undergo a significant reduction in volume under the combined action of heat and pressure. This shrinkage may represent more than 30% of the initial volume of the parts. Commonly employed methods currently enable these parts to be manufactured with tolerances on dimensions of around 0.5 to 1%, since the sintering step makes it difficult to obtain lower tolerances. It may be noted that these tolerances fluctuate according to the batches of raw material used.
By way of example, manufacturing tolerances involved by sintering operations may result in uncertainty of around 0.2 mm over the length of a 3 centimeter ceramic watch case. Given that ceramic watches are in the high end of watchmaking production, such uncertainties are difficult for manufacturers to accept.
To overcome this problem, the most commonly used solution for taking up play between the various ceramic elements used to make the watches consists in carrying out manual machining after the sintering step. However, faced with the increasing demand of clients for ceramic timepieces, manual machining steps have become more and more laborious given the number of timepieces to be treated. Further, manual machining steps are made even more difficult as the complexity of the geometry of the watch cases continues to increase.
It will be noted that the tolerance problem caused by sintering operations becomes more inconvenient the larger the dimensions of the external parts to be manufactured. In particular, these manufacturing tolerances have a detrimental effect on watch cases whose dimensions are generally greater than those of the bracelet links. It will also be clear that the more the manufacturers of ceramic watches wish to make bracelet links of large dimensions, the more difficulty they have in forming satisfactory attractive joins between the watch case and the bracelet or between the bracelet links.